The present invention relates to both dual use pins on an integrated circuit and to LED driver circuits.
As the size of integrated circuits (ICs) has decreased with advancing process technology, one limiting factor on the production of integrated circuits is the number of pins required to connect to the IC. There have been a large number of techniques used to keep the pin count down such that only necessary signals are used for pins. In addition, dual usage of pins is often implemented. For example, one pin might serve as an addressing pin at a first period in time, and subsequently function as the data output pin for the data which was addressed. Such multiplexing techniques are common.
In addition, pins can be used for programming an integrated circuit during an initial, start-up or programming mode. Subsequently, the pins can be used for normal functional input.backslash.output (I.backslash.O) during the functional usage of the IC. Examples of such circuits are set forth, for example, in U.S. Pat. No. 5,336,951 and U.S. Pat. No. 4,727,514.
One particular usage of a pin on an IC is to drive a light-emitting diode (LED) or other light-emitting device. Many electronic devices provide indicator lights to provide feedback to the user on the operation of the electronic device. Thus, pins are often dedicated to this function of driving the light-emitting diodes, which typically are not on the chip itself both because of their size and heat generation, and because of the need to locate them on the external chassis of the device where they can be viewed by the user, thus requiring a connection line between them and the IC.
Oftentimes, in more complicated systems, multiple ICs having LED drive pins may be connected to a single addressable management entity which activates the LEDs for different purposes in accordance with addresses assigned to the LEDs. Thus, each IC must determine whether an address is intended for its LED driver, and act appropriately.